The cerebellum consists of two hemispheres and a medial area called the vermis. The cerebellum is connected to other neural structures by three pairs of peduncles. The figure shows a dorsal view of the cerebellum, and the peduncles and cerebellar nuclei are obscured (shown by black areas).

Vermis

Hemisphere

Peduncles

Dentate nucleusInterposed

nucleus (emboliform and globose nuclei)

Fastigial nuclei

Lecture 15:Cerebellum

The cerebellum is divided into three lobes: the anterior lobe, the posterior lobe, and the flocculonodular lobe.

Cerebellar Lobes

Primary fissure Anterior lobe

Posterior lobe

Posteriorlateral fissure

Flocculonodular lobeNodulus

Flocculus

Somatotopical Projectionson the Cerebellum

The cerebellar cortex consists of three layers and five types of neurons. Inputs to the cerebellum are carried by mossy fibers (from the inferior olive) and by climbing fibers (from pontine nuclei, the vestibular system, and the spinal cord). The only output system of the cerebellum is the axons of Purkinje cells.

Neurons of the Cerebellum

Output (to cerebellar nuclei and then to thalamus, brain stem, and vestibular nuclei)

White matter

Molecular layer

Purkinje cell layer

Granular layer

Basket cell

Granule cell

Climbing fiber

Mossy fiber

Golgi cell

Stellate cell

Cerebellar Neurons

A single glomerulum consists of an incoming mossy fiber, clusters of small dendrites (called rosettes) from a few dozen granule cells, and the axons of the Golgi cells.

A Glomerulum

Mossy fiber

Golgi cell axon

Granule cell dendrites

Rosette

Excitatory inputs to the cerebellum are provided by mossy fibers and climbing fibers. The mossy fibers originate in the spinocerebellar tract and in brain stem nuclei; they excite granule cells. The climbing fibers originate in the medulla (the inferior olive); they make synapses on Purkinje cells.

Inputs Into the Cerebellum

Mossy fibers (spinocerebellar tract and brain stem nuclei)

Granule cells

Climbing fibers (inferior olive)

Purkinje cells

In response to a single excitatory stimulus, a Purkinje cell may generate

Simple and Complex Spikes

Simple spike

Complex spike

a single action potential (a simple spike, in response to mossy fiber input), or

a larger action potential, followed by a few smaller action potentials (a complex spike, in response to a signal from climbing fibers).

Stellate cells make inhibitory synapses on the dendrites of Purkinje cells. Parallel fibers activate Purkinje cells, basket cells, stellate cells, and Golgi cells. Basket cells inhibit relatively distant Purkinje cells. Golgi cells inhibit granular cells, decreasing their response to mossy fibers.

Wiring of the Cerebellum

Glomeruli

Parallel fibers

Golgi cells

Basket cells

Purkinje cells

Distant Purkinje cells

Stellate cells

Granular cellsMossy fibers

Climbing fiber

Neuronal Population Vectors of the PurkinjeCells and Neurons in the Cerebellar Nuclei

Cerebellar Memory?

If an action potential in a climbing fiber and another action potential in a parallel fiber arrive simultaneously at a Purkinje cell, the cell may “remember” this event with the help of a chemical mechanism, changing the synaptic efficacy.

Climbing fibers

Parallel fibers

Purkinje cell